U.S. patent number 10,538,269 [Application Number 15/288,026] was granted by the patent office on 2020-01-21 for steering system handwheel angle determination.
This patent grant is currently assigned to Steering Solutions IP Holding Corporation. The grantee listed for this patent is STEERING SOLUTIONS IP HOLDING CORPORATION. Invention is credited to Carl D. Tarum, Matthew A. Tompkins.
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United States Patent |
10,538,269 |
Tarum , et al. |
January 21, 2020 |
Steering system handwheel angle determination
Abstract
Technical solutions are described for estimating handwheel angle
of a steering wheel of a vehicle based on road wheel rotational
speed data. In one or more examples, the technical solutions are
used when the vehicle does not have a sensor to measure the
handwheel angle, or if the handwheel angle sensor is faulted and
unable to provide data on the actual handwheel angle.
Inventors: |
Tarum; Carl D. (Saginaw,
MI), Tompkins; Matthew A. (Saginaw, MI) |
Applicant: |
Name |
City |
State |
Country |
Type |
STEERING SOLUTIONS IP HOLDING CORPORATION |
Saginaw |
MI |
US |
|
|
Assignee: |
Steering Solutions IP Holding
Corporation (Saginaw, MA)
|
Family
ID: |
61695992 |
Appl.
No.: |
15/288,026 |
Filed: |
October 7, 2016 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20180099695 A1 |
Apr 12, 2018 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B62D
5/0484 (20130101); B62D 3/126 (20130101); B62D
15/024 (20130101); B62D 5/0487 (20130101); G01P
3/00 (20130101); B62D 5/049 (20130101) |
Current International
Class: |
B62D
15/00 (20060101); B62D 15/02 (20060101); B62D
5/04 (20060101); B62D 3/12 (20060101); G01P
3/00 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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103921841 |
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Jul 2014 |
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CN |
|
104428194 |
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Mar 2015 |
|
CN |
|
105579324 |
|
May 2016 |
|
CN |
|
105946971 |
|
Sep 2016 |
|
CN |
|
69118964 |
|
Dec 1996 |
|
DE |
|
19856304 |
|
Oct 1999 |
|
DE |
|
10003564 |
|
Aug 2001 |
|
DE |
|
102008021847 |
|
Nov 2009 |
|
DE |
|
102012012996 |
|
Jan 2013 |
|
DE |
|
Other References
English Translation of German Office Action for German Application
No. 102017122945.0 dated Aug. 3, 2018, 9 pages. cited by applicant
.
China National Intellectual Property Administration, The First
Office Action, Application No. 201710929603.3, dated Sep. 30, 2019.
cited by applicant.
|
Primary Examiner: Caputo; Lisa M
Assistant Examiner: Devito; Alex T
Claims
Having thus described the invention, it is claimed:
1. An electric power steering (EPS) system for computing handwheel
angle based on wheel speeds, the EPS system comprising: a handwheel
angle module configured to: receive a first wheel speed for a first
wheel; and receive a second wheel speed for a second wheel; a
calibration module configured to: compute a first calibration
factor based on the first wheel speed and the second wheel speed
using a predetermined model; compute a second calibration factor
based on an offset error in a wheel alignment sensor; wherein the
handwheel angle module is further configured to: receive the first
calibration factor and the second calibration factor from the
calibration module; and determine the handwheel angle based on the
first wheel speed, the second wheel speed, the first calibration
factor, and the second calibration factor based on .times..times.
.times..times. ##EQU00002## where HWA is the handwheel angle, R is
the first wheel speed, L is the second wheel speed, C1 is the first
calibration factor, and C2 is the second calibration factor.
2. The electric power steering (EPS) system of claim 1, wherein the
handwheel angle module determines the handwheel angle in response
to a vehicle-speed being below a predetermined threshold.
3. The electric power steering (EPS) system of claim 1, wherein the
handwheel angle module determines the handwheel angle in response
to a failure of a handwheel position sensor.
4. The electric power steering (EPS) system of claim 3, wherein the
handwheel angle module determines the handwheel angle further in
response to a failure of a motor position sensor.
5. The electric power steering (EPS) system of claim 1, wherein the
calibration module is configured to determine the first calibration
factor in response to a handwheel position sensor being
invalid.
6. The electric power steering (EPS) system of claim 1, wherein the
calibration factor module configured to determine the second
calibration factor in response to a handwheel position sensor being
invalid.
7. The electric power steering (EPS) system of claim 1, wherein the
first wheel is a front left wheel and the second wheel is a front
right wheel.
8. The electric power steering (EPS) system of claim 1, wherein the
first wheel speed and the second wheel speed are determined based
on one or more measured signals from the first wheel and the second
wheel respectively.
9. A system for determining handwheel angle in a steering system
based on wheel speeds, the system comprising: a handwheel angle
module configured to determine a state of a handwheel position
sensor, and in response to the handwheel position sensor being in
an invalid state: receive a first wheel speed for a first wheel;
receive a second wheel speed for a second wheel; determine a
handwheel angle based on the first wheel speed, the second wheel
speed, a first calibration factor, and a second calibration factor,
wherein the handwheel angle module determines the handwheel angle
based on .times..times..times..times. ##EQU00003## where HWA is the
handwheel angle, R is the first wheel speed, L is the second wheel
speed, C1 is the first calibration factor, and C2 is the second
calibration factor.
10. The system of claim 9, wherein the handwheel angle module
determines the handwheel angle in response to a vehicle-speed being
below a predetermined threshold.
11. The system of claim 9, further comprising a calibration module
configured to determine the first calibration factor based on the
first wheel speed and the second wheel speed in response to the
handwheel position sensor being in the invalid state.
12. The system of claim 9, further comprising a calibration module
configured to determine the second calibration factor based on an
offset error in a wheel alignment sensor in response to the
handwheel position sensor being in the invalid state.
13. The system of claim 9, wherein the first wheel speed and the
second wheel speed are determined based on one or more measured
signals from the first wheel and the second wheel respectively.
14. A steering system controller for determining a handwheel angle
in a steering system, the steering controller configured to: in
response to vehicle speed being below a predetermined threshold:
receive a first wheel speed for a first wheel; receive a second
wheel speed for a second wheel; compute a first calibration factor
based on the first wheel speed and the second wheel speed using a
predetermined model; compute a second calibration factor based on
an offset error in a wheel alignment sensor; and determine a
handwheel angle based on the first wheel speed, the second wheel
speed, the first calibration factor, and the second calibration
factor based on .times..times..times..times. ##EQU00004## where HWA
is the handwheel angle, R is the first wheel speed, L is the second
wheel speed, C1 is the first calibration factor, and C2 is the
second calibration factor.
15. The steering system controller of claim 14, further configured
to determine that a handwheel position sensor is in an invalid
state, and determining the handwheel angle responsively.
16. The steering system controller of claim 15, configured to
determine the first calibration factor based on the first wheel
speed and the second wheel speed in response to the handwheel
position sensor being in the invalid state.
17. The steering system controller of claim 15, configured to
determine the second calibration factor in response to the
handwheel position sensor being in the invalid state.
Description
TECHNICAL FIELD
The present application generally relates to electric power
steering (EPS) systems, and particularly to EPS systems that
facilitate rack and pinion limiting, by automatically determining
an angle of handwheel.
BACKGROUND
An electric power steering (EPS) system of a vehicle facilitates a
variety of steering functions and applications. For example,
steering functions include active return to a center position, rack
travel limit functions, and the like. Further, to prevent steering
parts of a suspension or tires to contact other parts of the
vehicle the EPS limits movement of a rack shaft of the EPS. Further
yet, applications of the EPS facilitate automated vehicle
functions, such as parking assist, where a vehicle, or an
electronic control unit (ECU) of a vehicle, sends messages and/or
commands to the EPS to turn to one or more handwheel angles to park
the vehicle. Thus, it is desirable to determine a current handwheel
angle of the EPS to provide above described and other steering
functions and applications.
SUMMARY
According to one or more embodiments, an electric power steering
(EPS) system for computing handwheel angle based on wheel speeds
includes a handwheel angle module. The handwheel angle module
receives a first wheel speed for a first wheel. The handwheel angle
module also receives a second wheel speed for a second wheel. The
handwheel angle module also determines the handwheel angle based on
the first wheel speed, the second wheel speed, a first calibration
factor, and a second calibration factor.
According to one or more embodiments, a system for determining
handwheel angle in a steering system based on wheel speeds includes
a handwheel angle module. The handwheel angle module determines a
state of a handwheel position sensor. In response to the handwheel
position sensor being in an invalid state, the handwheel angle
module receives a first wheel speed for a first wheel, and a second
wheel speed for a second wheel. The handwheel angle module also
determines a handwheel angle based on the first wheel speed, the
second wheel speed, a first calibration factor, and a second
calibration factor.
According to one or more embodiments, a steering system controller
for determining a handwheel angle in a steering system, in response
to vehicle speed being below a predetermined threshold, receives a
first wheel speed for a first wheel, and a second wheel speed for a
second wheel. The steering system controller also determines a
handwheel angle based on the first wheel speed, the second wheel
speed, a first calibration factor, and a second calibration
factor.
These and other advantages and features will become more apparent
from the following description taken in conjunction with the
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The subject matter that is regarded as the invention is
particularly pointed out and distinctly claimed in the claims at
the conclusion of the specification. The foregoing and other
features, and advantages of the invention are apparent from the
following detailed description taken in conjunction with the
accompanying drawings in which:
FIG. 1 depicts a schematic diagram of a motor control system in
accordance with exemplary embodiments;
FIG. 2 illustrates a block diagram of example components that
facilitate a steering system to determine a handwheel angle;
FIG. 3 illustrates a table for selecting a combination of wheel
speed signals for determining a calibration factor;
FIG. 4 illustrates examples of mathematical models that may be used
for determining a calibration factor; and
FIG. 5 illustrates a flowchart of an example method for providing
an HWA value for rack limiting and other steering applications.
DETAILED DESCRIPTION
As used herein the terms module and sub-module refer to one or more
processing circuits such as an application specific integrated
circuit (ASIC), an electronic circuit, a processor (shared,
dedicated, or group) and memory that executes one or more software
or firmware programs, a combinational logic circuit, and/or other
suitable components that provide the described functionality. As
can be appreciated, the sub-modules described below can be combined
and/or further partitioned.
The technical solutions described herein provide an electric power
steering (EPS) system that limits movement of a rack shaft of the
EPS, particularly in a sensor-less environment and at speeds below
a predetermined threshold, such as when a vehicle is being started.
In one or more examples, the EPS may have a predetermined limit
within which the rack shaft may move. Exceeding the limit may lead
to wheel/body contact, tie rod impact, and other conditions, which
may be detrimental to performance of the vehicle, and/or
inconvenience a user.
Accordingly, in one or more examples, technical solutions described
herein facilitate the EPS to limit the movement of the rack shaft
based on determining a center of a handwheel (steering wheel) of
the EPS, by determining handwheel angle (HWA) of the handwheel. The
handwheel angle may also be referred to as pinion angle. Typically,
the EPS uses sensors, such as a position sensor, which may be a
ring/spur gear, mounted in a steering gear or a steering column, to
determine the HWA. Alternatively, in case of an invalid state of
such sensors, such as absence or in case of a failure of the
sensors, the EPS estimates the HWA. For example, the EPS estimates
the HWA by monitoring a lateral acceleration and/or yaw rate while
the vehicle is being driven forward. Alternatively or in addition,
the EPS estimates the HWA by monitoring a driver handwheel torque,
vehicle speed, and changes to a position of a motor of the EPS
while the vehicle is being driven forward at highway speeds, such
as 20 KPH or higher.
However, the typical technical solutions used require that the
vehicle be in motion at least at a predetermined speed, such as 20
KPH or higher. Thus, at least in cases where the vehicle is at
lower speeds, such as when the vehicle is being started, or when
the vehicle is being parked, or other is being maneuvered at speeds
lower than the predetermined speed, without limiting the movement
of the rack shaft, the undesirable effects may occur. Accordingly,
the technical solutions described herein facilitate the EPS to
prevent tie rod impact, wheel/body contact, and other such effects
by limiting the rack at speeds lower than the predetermined speeds,
and further in a sensor-less environment.
Further, the typical technical solutions used take at least a few
seconds to estimate the HWA, and thus the center of the handwheel.
For example, the typical solutions use wheel speeds to calculate a
yaw, and then use the yaw to calculate the HWA. Accordingly, when
the vehicle is being started, the typical solutions may not prevent
the undesirable effect in case the user maneuvers the handwheel as
soon as the vehicle is started, because yaw may not be calculated.
The technical solutions described herein facilitate the EPS to
determine the HWA substantially instantaneously, by directly
computing the HWA at low speeds based on one or more vehicle
signals, and thus provide an improved rack movement limiting. For
example, the technical solutions described herein provide an
estimate of HWA within 90 degrees in less than 2 meters of vehicle
travel. In one or more examples, a vehicle signal may include
multiple data, such as multiple sensor or measurement data.
Thus, the technical solutions described herein facilitate an EPS
with a fast estimate of HWA to provide protection for rack
limitation, in case the sensors are in an invalid state, such as in
case of failure (or absence) of position sensors to detect the
HWA.
Referring now to the Figures, where the technical solutions will be
described with reference to specific embodiments, without limiting
same, FIG. 1 is an exemplary embodiment of a vehicle 10 including a
steering system 12 is illustrated. In various embodiments, the
steering system 12 includes a handwheel 14 coupled to a steering
shaft system 16 which includes steering column, intermediate shaft,
& the necessary joints. In one exemplary embodiment, the
steering system 12 is an EPS system that further includes a
steering assist unit 18 that couples to the steering shaft system
16 of the steering system 12, and to tie rods 20, 22 of the vehicle
10. Alternatively, steering assist unit 18 may be coupling the
upper portion of the steering shaft system 16 with the lower
portion of that system. The steering assist unit 18 includes, for
example, a rack and pinion steering mechanism (not shown) that may
be coupled through the steering shaft system 16 to a steering
actuator motor 19 and gearing. During operation, as a vehicle
operator turns the handwheel 14, the steering actuator motor 19
provides the assistance to move the tie rods 20, 22 that in turn
moves steering knuckles 24, 26, respectively, coupled to roadway
wheels 28, 30, respectively of the vehicle 10.
As shown in FIG. 1, the vehicle 10 further includes various sensors
31, 32, 33 that detect and measure observable conditions of the
steering system 12 and/or of the vehicle 10. The sensors 31, 32, 33
generate sensor signals based on the observable conditions. In one
example, the sensor 31 is a torque sensor that senses an input
driver handwheel torque (HWT) applied to the handwheel 14 by the
operator of the vehicle 10. The torque sensor generates a driver
torque signal based thereon. In another example, the sensor 32 is a
motor angle and speed sensor that senses a rotational angle as well
as a rotational speed of the steering actuator motor 19. In yet
another example, the sensor 32 is a handwheel position sensor that
senses a position of the handwheel 14. The sensor 33 generates a
handwheel position signal based thereon.
A control module 40 receives the one or more sensor signals input
from sensors 31, 32, 33, and may receive other inputs, such as a
vehicle speed signal 34. The control module 40 generates a command
signal to control the steering actuator motor 19 of the steering
system 12 based on one or more of the inputs and further based on
the steering control systems and methods of the present disclosure.
The steering control systems and methods of the present disclosure
apply signal conditioning and perform friction classification to
determine a surface friction level 42 as a control signal that can
be used to control aspects of the steering system 12 through the
steering assist unit 18. The surface friction level 42 can also be
sent as an alert to an ABS 44 and/or ESC system 46 indicating a
change in surface friction, which may be further classified as an
on-center slip (i.e., at lower handwheel angle) or an off-center
slip (i.e., at higher handwheel angle) as further described herein.
Communication with the ABS 44, ESC system 46, and other systems
(not depicted), can be performed using, for example, a controller
area network (CAN) bus or other vehicle network known in the art to
exchange signals such as the vehicle speed signal 34.
FIG. 2 illustrates a block diagram of example components that
facilitate the steering system 12 to determine the HWA, even at
speeds below the predetermined threshold. In one or more examples,
the components may be part of the control module 40. Alternatively
or in addition, the illustrated components may be separate from the
control module 40. The components include hardware, such as
electronic circuitry. In one or more examples, the components may
include non-transitory computer readable storage medium with
computer executable instructions embedded therein. In the
description that follows the components are described as being part
of the steering system 12, but it is understood that in other
examples, the components may be a separate system that communicates
with the steering system 12.
In one or more examples, the components include a HWA module 210, a
HWA sensor 220, a motor position sensor 230, a calibration module
240, a rack limiting module 250, and a steering application module
260 among others. One or more of the modules may communicate with
one another. For example, the HWA module 210 may receive status
messages from the HWA sensor 220, and the motor position sensor
230. Alternatively or in addition, the HWA module 210 receives one
or more calibration factor values from the calibration module 240.
Further, the HWA module 210 may output HWA value(s) to the rack
limiting module 250 and the steering application module 260.
In one or more examples, the rack limiting module 250 limits the
movement of the rack shaft according to the HWA value output by the
HWA module 210. For example, the rack limiting module 250
determines if an end-of-travel (EOT) condition is met based on the
HWA estimate from the HWA module 210. In one or more examples, the
EOT condition may be a threshold HWA with respect to a center
position of the handwheel 14. As described herein, the rack
limiting module 250, based on the HWA estimate, prevents the rack
shaft of the steering system 12 to travel beyond the predetermined
limits, thus preventing possible damage such as tires (wheels)
rubbing against other fender, or other parts of the vehicle,
tie-rod impact, and the like.
Further, the steering application module 260 receives the HWA
estimate from the HWA module 210. The steering application module
260 uses the HWA estimate for one or more steering application,
such as parking control, handwheel return assist, or any other
autonomous or semi-autonomous control of the handwheel 14 of the
steering system 12. It is understood that the components may
include additional steering application modules that receive the
HWA estimate value as input.
In one or more examples, the HWA sensor 220 and the motor position
sensor 230 may be one or more of the sensors 33. Alternatively, the
HWA sensor 220 and the motor position sensor 230 may be additional
sensors. The HWA sensor 220 may identify the HWA of the handwheel
14. In one or more examples, the HWA sensor 220 may include one or
more sensors. In one or more examples, the HWA sensor 220 sends the
HWA value to the HWA module 210, which in turn relays the
information to other modules that receive the HWA value as input.
In one or more examples, the HWA module 210 uses the sensor
information from the HWA sensor 220 to compute the HWA estimate
value. The HWA sensor 220 additionally indicates, to the HWA module
210, a status of the HWA sensor 220. For example, the HWA sensor
220 may experience a failure, such as low battery, or any other
failure. Alternatively or in addition, the HWA sensor 220 may not
be operable until a specific vehicle speed is reached, and thus
during ignition of the vehicle, the HWA sensor 220 may indicate a
failure condition. Accordingly, in one or more examples, in
response to the HWA sensor 220 indicating a failure condition, the
HWA module 210 computes the HWA estimate value.
In one or more examples, the motor position sensor 230 identifies
and relays information about the position of the motor 19 of the
steering system 12. In one or more examples, the motor position
sensor 230 transmits the sensor information to the HWA module 210.
For example, in case the HWA sensor 220 is in condition of failure,
or if the steering system 12 is not equipped with the HWA sensor
220, the HWA module 210 estimates the HWA value based on the
information from the motor position sensor 230. In one or more
examples, the HWA module 210 accesses the information from the
motor position sensor 230 in response to detecting a failure of the
HWA sensor 220. Alternatively or in addition, the motor position
sensor 230 continuously transmits the motor position to the HWA
module 210, such as at a predetermined frequency. In one or more
examples, the HWA may be determined as a ratio of motor pinion
angle added with an offset that the HWA module 210 determines. The
ratio of the motor pinion angle may be 25:1, or any other ratio
specific to the vehicle and/or the steering system 12. Accordingly,
the HWA module 210 determines the HWA angle based on the
information from the motor position sensor.
The HWA module 210, further receives as input, wheel speed signals.
The wheel speed signals may provide a speed value or a
rotation-count value for one or more of the wheels (tires) of the
vehicle 10. In one or more examples, the HWA module 210 computes
the wheel speed using the rotation-count value. For example, the
HWA module 210 uses a predetermined conversion factor that is
specific for the vehicle 10, such as 32 counts per KPH, or the
like. In one or more examples, the wheel speed signals broadcast 0
(zero) until a predetermined threshold, such as 22 counts (0.6875
KPH), or any other predetermined threshold.
The HWA module 210 further receives one or more calibration factors
from the calibration module 240. In one or more examples, the
calibration module 240 may provide a predetermined calibration
factor. Alternatively or in addition, the calibration module 240
computes the one or more calibration factors as the steering system
12 is being operated. In one or more examples, the calibration
module 240 stores the computed calibration factors and provides the
values to the HWA module 210 in response to a corresponding request
from the HWA module 210.
Based on the inputs, the HWA module 210 estimates the HWA value
when the HWA sensor 220 and/or the motor position sensor 230 are
absent or in failure condition. In one or more examples, the HWA
module 210 estimates the HWA value at low speeds, such as below a
predetermined threshold, as described herein. In one or more
examples, the HWA module 210 estimates the HWA value using an
equation such as,
.times..times..times..times..times..times. ##EQU00001## where HWA
is the handwheel angle (or pinion angle) in degrees, R_ND is the
right non-driven wheel speed, L_ND is the left non-driven wheel
speed, C1 is a first calibration factor in degrees, and C2 is a
second calibration factor in degrees. In a two wheel drive vehicle,
the "Driven" wheels are the ones driven by the transmission, and
the "Non-Driven" are the wheels that are not connected to the
drivetrain. For example, in case of a rear-wheel drive vehicle such
as a pickup truck, the rear wheels may be the driven wheels, and
the front wheels the non-driven. In case of a front-wheel drive
vehicle such as a car, the front wheels are the driven wheels, and
the rear wheels are the non-driven. In the example scenario used
herein, the powertrain may only drive the rear wheels, so the front
wheels are Non-Driven. It is understood that in other examples,
other combinations of wheel speeds can be used, as shown in FIG.
3.
In one or more examples, the calibration module 240 computes the
first calibration factor C1 as a relationship between two wheel
speeds of the vehicle 10. The value of C1 may be specific to the
vehicle 10. For example, the calibration module 240 determines C1
based on tire wear, wheel changes, vehicle customization, and the
like. In one or more examples, the calibration module 240 stores a
default value for C1 and updates the value as the steering system
12 is maneuvered. For example, when the steering system 12 is being
operated, without a failure condition, the calibration module
determines a relationship between the wheel speeds and the HWA
value that the HWA sensor provides. For example, the calibration
module 240 determines the first calibration factor C1 when a
vehicle speed is less than a predetermined threshold, such as 20
KPH. Alternatively or in addition, the calibration module 240
determines C1 when the HWA value from the HWA sensor 220 is more
than 90 degrees. Alternatively or in addition, the calibration
module 240 determines C1 when L_ND and R_ND are different from each
other by a predetermined value, such as at least 0.3 KPH. In one or
more examples, the calibration module 240 ensures that the L_ND and
R_ND values are valid by comparing the values on multiple
intra-vehicle communication networks. The calibration module 240
may further ensure that the HWA sensor 210 is valid, that is not in
a failure condition, prior to using the HWA value for determining
C1
In one or more examples, the calibration module 240 determines C1
based on a predetermined model, such as a linear model, a parabolic
model, or the like. The predetermined model to be used may depend
on the two signals from the wheel speed signals used for
determining C1. For example, a pair of signals may be selected for
determining C1. In case the vehicle 10 is equipped with four
wheels, the wheel speed signals received may include signals from a
left front wheel, a right front wheel, a left rear wheel, and a
right rear wheel. If the vehicle 10 is equipped with additional
wheels, the wheel speed signals may include additional signals. The
steering system 12 may be a front-wheel, rear-wheel, or an
all-wheel drive system. The table in FIG. 3 illustrates different
combinations of the wheel signals that the calibration module 240
uses to determine C1. For example, the calibration module 240 may
use the wheel speed signals from the left front wheel 310 and the
right front wheel 320 (Case 1). Alternatively or in addition, the
calibration module 240 uses the wheel speed signals from the left
front wheel 310 and the right rear wheel 340 (Case 4). As
illustrated, any other combination of the wheel speed signals may
be used for determining C1.
In one or more examples, the calibration module 240 determines C1
based on the selected pair of wheel signals. The calibration module
240 determines C1 to determine the HWA based on a difference
between the wheel speeds. For example, if the driver is making a
right turn, the wheel speed of the right front wheel 330 may be
faster or slower than the left rear wheel 330, depending on the
handwheel angle. On either right or left turn, the rear wheels
track inside of the front wheel on the same side, and have a slower
wheel speed. The calibration module 240 determines a relationship
between the handwheel angle and the difference in the wheel
speeds.
In one or more examples, the calibration module 240 selects a
predetermined mathematical model to calculate C1 based on the
wheels signals being used for determining the C1. FIG. 4
illustrates examples of mathematical models that may be used for
determining C1. For example, the calibration module 240 uses a
linear model for determining C1 if the pair of signals being used
includes only front wheel signals, or only rear wheel signals. The
calibration module 240 may use a parabolic model if cross-wheel
signals are used, that is the pair of signals includes one front
wheel signal and one rear wheel signal. It is understood, that
above selections of the mathematical model are examples and that
different examples may use a different selection.
In one or more examples, the calibration module 240 computes C1 on
a periodic basis. In one or more examples, the calibration module
240 stores the most recent computed value of C1 to output to the
HWA module 210 for estimating the HWA. Alternatively or in
addition, the calibration module 240 computes a new C1 value based
on the most recent computed C1 value and a previously stored C1
value, for example by averaging the two values, and stores the new
C1 value. For example, if C1.sub.t-1 is the stored value, and if C1
.sub.t-temp is the value the most recent computed value, the
calibration module 240 computes C.sub.t by averaging C1.sub.t-1 and
C1.sub.t-temp, and stores C1.sub.t in place of C1.sub.t-1.
In one or more examples, the calibration module 240 determines C1
values based on more than one pair of signals and computes and
stores an average of the computed values.
In one or more examples, the second calibration factor C2 may be a
HWA sensor offset error from alignment, that the calibration module
240 computes during the operation of the steering system 12. For
example, the HWA value from the HWA sensor 220 may not be 0 (zero)
when the vehicle 10 is driving straight. For example, the
difference (from 0) may be due to an error in wheel alignment, or
an error in alignment of the steering system 12 and the wheels of
the vehicle. Accordingly, C2 is an offset such that the resulting
HWA is 0 degrees when the vehicle 10 is driving straight. In one or
more examples, the value of C2 is 0 (zero) by default, and is
updated as the vehicle 10 is driven. For example, C2 may be
determined when, for at least 10 messages of the wheel signals,
L_ND and R_ND are above a predetermined speed value, such as 60
KPH, the L_ND and R_ND are within a predetermined threshold, such
as 0.25 KPH, and when the handwheel gradient is substantially zero.
The handwheel gradient is the velocity of the handwheel of the
steering system 12, in degrees/second. In response to the above
conditions, the calibration module 240 stores the HWA value from
the HWA sensor 220 as the value of C2.
Thus, using the calibration factors C1 and C2, the HWA module 210
provides a fast, coarse estimate of handwheel angle, such as to
provide for protection to the rack limiting module 250 and the
other steering application module 260. For example, the HWA module
210 estimates the HWA within 90 degrees in less than 2 meters of
vehicle travel. As described herein, the HWA module 210 generates
the HWA estimate in response to the HWA sensor 220 being absent or
in failure, and further the vehicle speed being below the
predetermined threshold.
In one or more examples, the HWA module 210 generates a separate
signal, referred to as HWA authority signal, that indicates whether
to use the HWA estimate from the HWA module 210. For example, the
HWA authority signal may be set at value 0 (zero) at vehicle
startup. Once all vehicle speed signals are above a threshold, such
as 1 KPH, the HWA module 210 estimates the HWA and sets the HWA
authority to a value of 0.1, or the like (below 1). The HWA
estimation and the HWA authority signal may be setup irrespective
of whether the vehicle 10 is moving forward or in reverse
direction. In one or more examples, the steering application module
260, and the rack limiting module 250 is enabled based on the HWA
authority signal being greater than 0. Accordingly, once the HWA
has been estimated, the HWA module 210 configures the HWA authority
signal to a positive non-zero value to so that the rack limiting
module 250 initiates the protection for end-of-travel and or the
rack limiting before end of travel is reached. Because the
estimated HWA value may be off (such as by 50 degrees), the HWA
authority signal is not set to 1 (or any other value) that
indicates that the HWA value is accurate. Instead, by setting the
HWA value to less than 1 (such as 0.1), the HWA module 210
indicates that the HWA value is an estimate.
It is understood that even though the HWA module 210 indicates that
the HWA value is an estimate, one or more functions can use the HWA
value to improve performance. For example, in case of the active
return function, when vehicle speed is greater than 0 and less than
a predetermined threshold, and when the handwheel angle is not 0
degrees, the steering system 12 applies a torque to return the
handwheel back to center, or to 0 degrees. In case the HWA
authority is not=1, the return function will be scaled so that at
least some returnability function is included.
Once vehicle speeds signals are above a predetermined threshold,
such as 10 KPH, the HWA value is determined based on the HWA sensor
220 and/or the motor position sensor 230, and the HW authority
signal is set to 1 (or any other value) to indicate that the HWA
value is accurate. The HWA for the rest of the ignition cycle is
based on the motor position sensor 230, unless the motor position
sensor 230 indicates a failure.
Further, the HWA value from the HWA module 210 depends on the
vehicle speed, and thus wheel speed. For example, consider that at
1 KPH and near a corner, a 1 rotation-count difference in wheel
speed (between front left and front right wheels), changes the HWA
by 62 degrees based on the C1 and C2 calibration factors from the
calibration module 240. At 10 KPH, the 1 rotation-count difference
may change the HWA by 6.2 degrees, and at 100 KPH, the difference
may represent an HWA change of 0.62 degrees.
FIG. 5 illustrates a flowchart of an example method for providing
an HWA value for rack limiting and other steering applications. The
method may be implemented by the HWA module 210. In one or more
examples, the HWA module may be part of the control module 40. The
HWA module 210 determines if HWA is to be estimated, as shown at
block 510. The HWA module 210 determines that the HWA is to be
estimated based on one or more of a state of the HWA sensor 220,
the motor position sensor 230, and the vehicle speeds. For example,
the HWA module 210 estimates the HWA in response to the vehicle
ignition cycle in progress.
If the HWA is to be estimated, the HWA module 210 computes the HWA
estimate value, as shown at block 520. As described herein, the HWA
module 210 determines the HWA estimate value based on the Equation
1. While Equation 1 uses individual wheel speeds, the HWA module
210 computes the HWA from any other vehicle signal that produces a
relative road wheel rotational position or rotational speed, such
as ABS pulse counts, transmission shaft speed or rotation angle,
wheel frequencies, and any other vehicle data that can be converted
to an individual wheel speed. Further, the HWA estimate value may
be determined while the vehicle 10 is moving forward or in reverse.
Further, the HWA module 210 estimates the HWA even when the
steering system is maneuvered in a static position, that is, at 0
KPH vehicle speed. The HWA module further sets up the HWA authority
signal to indicate HWA value is an estimate, as shown at block 530.
For example, the HWA module 210 sets up the HWA authority signal to
a value between 0 and 1, if 1 indicates that the HWA value is
accurate and 0 indicates that the HWA value is not determined.
Instead, if the HWA value is not to be estimated, the HWA module
210 determines the HWA value based on input from the HWA sensor 220
and/or the motor position sensor 230, as shown at block 540. The
HWA module 210 further sets up the HWA authority signal to indicate
HWA value is accurate, such as by setting the signal to 1, as shown
at block 550. In addition, the calibration module 240 determines
and stores the first calibration factor C1, as shown at block 560.
The calibration module 240 determines the value for C1 specific to
the vehicle 10, as described herein. Further, calibration module
240 determines and stores the second calibration factor C2 as
described herein, as shown at block 570.
The HWA module 210 further outputs the computed HWA value and the
HWA authority signal value, as shown at block 580. In one or more
examples, the rack limiting module 250 and/or the steering
application module 260 receives the HWA value and the HWA authority
signal for corresponding operations.
In other words, the control module 40 determines whether to
estimate the HWA, at block 510. If yes, then the control module
computes the HWA as described herein, at block 520. The HWA
authority value is set to indicate a quality of the HWA, at block
530. This may be set to 0.0 before the vehicle is in motion. Then
an initial calculation of HWA at low speeds may set the authority
to 0.2. After driving a predetermined time at least a predetermined
(highway) speeds, the authority may be set to 1.0. Other functions,
such as active return, may limit the response based on the
handwheel authority. If block 510 determines that the HWA can be
measured (and not estimated) using one or more sensors, then the
control module determines the HWA and handwheel authority from the
sensor data, at blocks 540 and 550. Further, at blocks 560 and 570,
the control module determines the calibration factors C1 & C2
and stores the calibration factors. Further yet, at block 580 the
HWA and the handwheel authority is output and/or stored.
Accordingly, the technical solutions described herein facilitate a
steering system, such as an EPS, to provide an estimated handwheel
angle for functions such as active return to center and rack travel
limiting in case of low vehicle speeds and/or when one or more
sensors that provide the handwheel angle are absent or in a state
of failure. The technical solutions described herein facilitate
determining the handwheel angle based on differences between wheel
speeds by determining one or more calibration factors during
operation of the vehicle. Accordingly, the handwheel angle can be
estimated when the vehicle is being started, or when the vehicle is
being parked (low speeds) and facilitate functions such as rack
limiting and end-of-travel protection even at low speeds based on
the estimated handwheel angle.
As described herein, the handwheel angle, or the pinion angle may
be computed from the formula: HWA=C1*(R-L)/(R+L)+C2, where HWA is
the Handwheel angle, R & L are right and left wheel speeds, and
C1, C2 are calibration factors specific for a vehicle. If the HWA
is not known (initial start up with sensorless system, or sensor
fault), the wheel speeds and calibration factors are used to
calculate the HWA. Wheel speeds may be in kph, rpm, Hertz, or any
other measurement that describes wheel rotation. The calibration
factors are determined from the wheel speeds and their relationship
to the HWA, which is based on the mechanical design of the
vehicle.
The calibration factors are initially established based on data
from functional sensors. C1 is used to convert the ratio of wheel
speeds to the handwheel angle. C2, which may typically be zero, is
included for use where wheel speeds may not be as expected. For
example, the vehicle usage wears down one tire faster than the
other, so that when the vehicle is being driven straight ahead, the
individual wheel speeds are different. In another example, a
compact spare tire may be installed, which is significantly smaller
than the other wheel. For such examples, the computation of the
handwheel angle is adjusted by C2 to offset the handwheel angle to
0 degrees (center position) when the vehicle is being driven
straight.
The present technical solutions may be a system, a method, and/or a
computer program product at any possible technical detail level of
integration. The computer program product may include a computer
readable storage medium (or media) having computer readable program
instructions thereon for causing a processor to carry out aspects
of the present technical solutions.
Aspects of the present technical solutions are described herein
with reference to flowchart illustrations and/or block diagrams of
methods, apparatus (systems), and computer program products
according to embodiments of the technical solutions. It will be
understood that each block of the flowchart illustrations and/or
block diagrams, and combinations of blocks in the flowchart
illustrations and/or block diagrams, can be implemented by computer
readable program instructions.
The flowchart and block diagrams in the Figures illustrate the
architecture, functionality, and operation of possible
implementations of systems, methods, and computer program products
according to various embodiments of the present technical
solutions. In this regard, each block in the flowchart or block
diagrams may represent a module, segment, or portion of
instructions, which comprises one or more executable instructions
for implementing the specified logical function(s). In some
alternative implementations, the functions noted in the blocks may
occur out of the order noted in the Figures. For example, two
blocks shown in succession, in fact, may be executed substantially
concurrently, or the blocks may sometimes be executed in the
reverse order, depending upon the functionality involved. It will
also be noted that each block of the block diagrams and/or
flowchart illustration, and combinations of blocks in the block
diagrams and/or flowchart illustration, can be implemented by
special purpose hardware-based systems that perform the specified
functions or acts or carry out combinations of special purpose
hardware and computer instructions.
It will also be appreciated that any module, unit, component,
server, computer, terminal or device exemplified herein that
executes instructions may include or otherwise have access to
computer readable media such as storage media, computer storage
media, or data storage devices (removable and/or non-removable)
such as, for example, magnetic disks, optical disks, or tape.
Computer storage media may include volatile and non-volatile,
removable and non-removable media implemented in any method or
technology for storage of information, such as computer readable
instructions, data structures, program modules, or other data. Such
computer storage media may be part of the device or accessible or
connectable thereto. Any application or module herein described may
be implemented using computer readable/executable instructions that
may be stored or otherwise held by such computer readable
media.
While the technical solutions are described in detail in connection
with only a limited number of embodiments, it should be readily
understood that the technical solutions are not limited to such
disclosed embodiments. Rather, the technical solutions can be
modified to incorporate any number of variations, alterations,
substitutions, or equivalent arrangements not heretofore described,
but which are commensurate with the spirit and scope of the
technical solutions. Additionally, while various embodiments of the
technical solutions have been described, it is to be understood
that aspects of the technical solutions may include only some of
the described embodiments. Accordingly, the technical solutions are
not to be seen as limited by the foregoing description.
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